The invention relates to a circuit arrangement for coupling a communication device having at least one unidirectional transmission channel and at least one unidirectional receive channel to a bidirectional communication device having at least one differential amplifier.
Such a circuit arrangement provides, more particularly, a hybrid circuit for splitting up a bidirectional communication device (for example a two-wire link) transmitting both the transmission channel and the receive channel, in a communication device having a separate, unidirectional transmission channel and receive channel (for example, a four-wire link), which communication device simultaneously provides a suitable amplification of the decoupled transmit and receiving channels. Hybrid circuits can be included at any place where transmission paths have to be split up within communication networks. For example, within the coverage area of telephone networks, two-wire links are used especially for reasons of cost-saving, the two directions running over a pair of lines. For amplifying the signals on trunk lines in both directions, a four-wire link with a line pair for either direction and the respective amplifiers is to be split up. Also when a subscriber terminal is to be connected to the local network, the directions of transmission and reception (microphone and loudspeaker) inside the device are to be separated.
The object of the invention is to provide a circuit arrangement of the type defined in the opening paragraph which optimizes the properties of the coupling with the simplest possible means.
The object is achieved in that the control inputs of the differential amplifier are coupled to the outputs of a transmission channel, the outputs of the differential amplifier to the bidirectional communication device, and the negative feedback path of the differential amplifier is coupled to an input of a receive channel, a matching impedance being provided in its negative feedback path for adjusting a DC voltage/DC current characteristic for the circuit arrangement when connected to the bidirectional communication device.
Preferred embodiments representing particularly advantageous embodiments of the invention can be taken from the patent claims and the description of the examples of embodiment.